summaryrefslogtreecommitdiff
path: root/src/mongo/db/geo/r2_region_coverer.h
blob: ef7f66c736800c4bbafe1391a8bfd8f4d741735a (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159

/**
 *    Copyright (C) 2018-present MongoDB, Inc.
 *
 *    This program is free software: you can redistribute it and/or modify
 *    it under the terms of the Server Side Public License, version 1,
 *    as published by MongoDB, Inc.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    Server Side Public License for more details.
 *
 *    You should have received a copy of the Server Side Public License
 *    along with this program. If not, see
 *    <http://www.mongodb.com/licensing/server-side-public-license>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the Server Side Public License in all respects for
 *    all of the code used other than as permitted herein. If you modify file(s)
 *    with this exception, you may extend this exception to your version of the
 *    file(s), but you are not obligated to do so. If you do not wish to do so,
 *    delete this exception statement from your version. If you delete this
 *    exception statement from all source files in the program, then also delete
 *    it in the license file.
 */

#pragma once

#include <boost/noncopyable.hpp>
#include <boost/scoped_ptr.hpp>
#include <queue>
#include <vector>

#include "mongo/db/geo/hash.h"


namespace mongo {

class R2Region;

class R2RegionCoverer : boost::noncopyable {
    // By default, the covering uses at most 8 cells at any level.
    static const int kDefaultMaxCells;  // = 8;

public:
    R2RegionCoverer(GeoHashConverter* hashConverter);
    ~R2RegionCoverer();

    // Set the minimum and maximum cell level to be used.  The default is to use
    // all cell levels.  Requires: max_level() >= min_level().
    void setMinLevel(unsigned int minLevel);
    void setMaxLevel(unsigned int maxLevel);
    unsigned int minLevel() const {
        return _minLevel;
    }
    unsigned int maxLevel() const {
        return _maxLevel;
    }

    // Sets the maximum desired number of cells in the approximation (defaults
    // to kDefaultMaxCells).
    //
    // For any setting of max_cells(), an arbitrary number of cells may be
    // returned if min_level() is too high for the region being approximated.
    //
    // TODO(sz): accuracy experiments similar to S2RegionCoverer.
    void setMaxCells(int maxCells);
    int maxCells() const {
        return _maxCells;
    }

    void getCovering(const R2Region& region, std::vector<GeoHash>* cover);

private:
    struct Candidate {
        GeoHash cell;
        bool isTerminal;  // Cell should not be expanded further.
        int numChildren;  // Number of children that intersect the region.
        Candidate* children[4];
    };

    // If the cell intersects the given region, return a new candidate with no
    // children, otherwise return NULL.  Also marks the candidate as "terminal"
    // if it should not be expanded further.
    Candidate* newCandidate(GeoHash const& cell);

    // Process a candidate by either adding it to the result_ vector or
    // expanding its children and inserting it into the priority queue.
    // Passing an argument of NULL does nothing.
    void addCandidate(Candidate* candidate);

    // Free the memory associated with a candidate.
    void deleteCandidate(Candidate* candidate, bool freeChildren);

    // Populate the children of "candidate" by expanding from the given cell.
    // Returns the number of children that were marked "terminal".
    int expandChildren(Candidate* candidate);

    // Computes a set of initial candidates that cover the given region.
    void getInitialCandidates();

    GeoHashConverter* _hashConverter;  // Not owned.
    // min / max level as unsigned so as to be consistent with GeoHash
    unsigned int _minLevel;
    unsigned int _maxLevel;
    int _maxCells;

    // Save the copy of pointer temporarily to avoid passing this parameter internally.
    // Only valid for the duration of a single getCovering() call.
    R2Region const* _region;

    // We keep the candidates that may intersect with this region in a priority queue.
    struct CompareQueueEntries;
    typedef std::pair<int, Candidate*> QueueEntry;
    typedef std::priority_queue<QueueEntry, std::vector<QueueEntry>, CompareQueueEntries>
        CandidateQueue;
    boost::scoped_ptr<CandidateQueue> _candidateQueue;  // Priority queue owns candidate pointers.
    boost::scoped_ptr<std::vector<GeoHash>> _results;
};


// An R2CellUnion is a region consisting of cells of various sizes.
class R2CellUnion : boost::noncopyable {
public:
    void init(const std::vector<GeoHash>& cellIds);
    // Returns true if the cell union contains the given cell id.
    bool contains(const GeoHash cellId) const;
    // Return true if the cell union intersects the given cell id.
    bool intersects(const GeoHash cellId) const;
    std::string toString() const;

    // Direct access to the underlying vector.
    std::vector<GeoHash> const& cellIds() const {
        return _cellIds;
    }

    // Swaps _cellIds with the given vector of cellIds.
    void detach(std::vector<GeoHash>* cellIds);

    // Adds the cells to _cellIds and calls normalize().
    void add(const std::vector<GeoHash>& cellIds);

    // Subtracts cellUnion from *this
    void getDifference(const R2CellUnion& cellUnion);

private:
    // Normalizes the cell union by discarding cells that are contained by other
    // cells, replacing groups of 4 child cells by their parent cell whenever
    // possible, and sorting all the cell ids in increasing order.  Returns true
    // if the number of cells was reduced.
    bool normalize();
    std::vector<GeoHash> _cellIds;
};

} /* namespace mongo */